The present invention relates to a variable vibration isolating support device for supporting an internal combustion engine while controlling the vibration of the internal combustion engine, and a technique to control the idling speed of an internal combustion engine to which an air pressure actuation mechanism such as a variable vibration isolating support device is mounted side by side.
Generally, an internal combustion engine mounted on an automobile or the like has a cylinder block with a plurality of cylinders, and a cylinder head fixed to the cylinder block. In the cylinder block, a plurality of cylinders are formed, and in each cylinder, a piston which can freely reciprocate is loaded. The piston of each cylinder is connected to a crank shaft rotatably supported in the cylinder block through a connecting rod, so that the reciprocating motion of the piston may be changed into the rotational movement of the crank shaft.
In each cylinder, a combustion chamber enclosed by the upper surface of the piston, the inner wall of the cylinder, and the cylinder head is formed. In the cylinder head, an intake port and an exhaust port are formed so that the opening ends thereof may face the combustion chamber. Furthermore, to the cylinder head, a spark plug is attached, facing the combustion chamber of each cylinder.
The intake port leads to an intake branch tube attached to the cylinder head. The intake branch tube leads to an air cleaner box through an intake tube. To each branch tube of the intake branch tube, a fuel injection valve is attached so that the injection hole thereof may face the intake port.
The exhaust port leads to an exhaust branch tube attached to the cylinder head. The exhaust branch tube leads to a muffler through an exhaust tube. In the course of the exhaust tube, an exhaust gas purifying catalyst for purifying the injurious ingredients in the exhaust gas is mounted.
In the internal combustion engine arranged like this, the piston descends so that the pressure in the combustion chamber may be negative, in the cylinder at the intake stroke. The negative pressure is applied to the intake tube through the intake port and the intake branch tube. The fresh air taken in the intake tube through the air cleaner box flows to the intake branch tube by receiving the negative pressure, and next flows to the intake port. The fresh air flowing into the intake port is sucked into the combustion chamber while forming gaseous mixture by being mixed with the fuel injected from the fuel injection valve.
When the cylinder has moved from the intake stroke to the compression stroke, the piston rises so that the gaseous mixture filled in the combustion chamber may be compressed. The compressed gaseous mixture is fired by the spark plug and explodes. The explosion power of the gaseous mixture presses down the piston. At this time, the cylinder moves from the compression stroke to the explosion stroke.
In the cylinder in which the explosion stroke has finished, the piston rises again so that the burned gas in the combustion chamber may be discharged to the exhaust port. The burned gas (exhaust gas) discharged to the exhaust port is introduced to the exhaust tube through the exhaust branch tube, and is purified at the exhaust gas purifying catalyst mounted in the course of the exhaust tube. The exhaust gas purified at the exhaust gas purifying catalyst is released into the atmosphere through the exhaust tube and the muffler.
In an internal combustion engine, for controlling the amount of fresh air supplied into the combustion chamber, a throttle valve is provided in the course of the intake tube. Moreover, to the intake tube, a bypass passage making a detour around the throttle valve is attached, and to the bypass passage, an idling speed control valve (ISCV) for controlling the flow rate in the bypass passage is mounted.
At the time of idling when the throttle valve is entirely closed, the ISCV is opened so that fresh air may be supplied to the combustion chamber of each cylinder. The opening of the ISCV is determined so that the idling speed of the internal combustion chamber may be a desired target idling speed.
By using the ISCV, even at the time of idling when the throttle valve is entirely closed, a desired amount of fresh air can be supplied to the internal combustion engine, and the operating condition of the internal combustion engine can be made to be stable.
On the other hand, in a case where the internal combustion engine is mounted on a body, for preventing various types of vibrations such as an idling vibration of an internal combustion engine or an engine shake from being transmitted to the body side, a variable vibration isolating support device which changes the vibration isolating characteristics according to the various types of vibrations, is used.
As a variable vibration isolating support device, for example, a liquid sealing type vibration isolating device described in JP U Hei4-77041, an active mount described in JP A Hei6-16050, and the like are well known.
The liquid sealing type vibration isolating device described in Japanese Utility Model Application Laid-Open (JP-U) No. Hei4-77041 comprises: a hydraulic liquid chamber made in such a way that a part of the chamber wall is formed by a vibration isolating base body made of an elastic body; a first compensating liquid chamber leading to the hydraulic liquid chamber through a first orifice and made in such a way that a part of the chamber wall is formed by a first diaphragm; a first air chamber separated from the first compensating liquid chamber by the first diaphragm; a second compensating liquid chamber leading to the hydraulic liquid chamber through a second orifice and made in such a way that a part of the chamber wall is formed by a second diaphragm; and a second air chamber separated from the second compensating liquid chamber by the second diaphragm.
The second orifice is formed such that the diameter thereof is larger than that of the first orifice. It is arranged that the atmospheric pressure is introduced into the first air chamber at all times and into the second air chamber, the negative pressure and the atmospheric pressure are selectively introduced.
As the method to selectively introduce the atmospheric pressure and the negative pressure into the second air chamber, while connecting a negative pressure passage to the intake passage of the internal combustion engine on the down stream of the throttle valve, an atmospheric passage is connected to the intake passage on the upper stream side of the throttle valve, and the negative pressure passage, the atmospheric passage, and the second air chamber are connected through a three way switching valve.
The three way switching valve comprises: a valve body for switching between the continuity of the negative pressure passage and the second air chamber (closing of the atmosphere passage), and the continuity of the atmosphere passage and the second air chamber (closing of the negative pressure passage); and an electromagnetic solenoid for driving the valve body, and the electromagnetic solenoid drives the valve body according to the driving pulse signal corresponding to the ratio of the time of continuity of the negative pressure passage and the second air chamber, to the time of continuity of the atmosphere passage and the second air chamber (duty ratio).
In this case, into the air chamber, the atmosphere flowing in the intake passage on the upper stream side of the throttle valve, and the intake tube negative pressure produced in the intake passage on the down stream side of the throttle valve are selectively introduced.
For example, when decreasing comparatively high frequency vibrations such as an idling vibration, the liquid sealing type vibration isolating device makes the volume of the second compensating liquid chamber variable, and decreases the dynamic spring constant of the whole system, by introducing the atmosphere into the second air chamber to make the diaphragm be in a movable state.
When decreasing comparatively low frequency vibrations such as an engine shake, the liquid sealing type vibration isolating device makes the volume of the second compensating liquid chamber constant, and increases the damping coefficient of the whole system, by introducing the negative pressure into the second air chamber to adhere the diaphragm to the wall surface.
Next, the active mount described in JP A Hei6-16050 has a rubber member and a liquid sealing portion connected by a variable orifice, and is arranged such that the opening area of the opening portion of the variable orifice is variable according to the vibration characteristics.
The active mount estimates the cylinder reaching the explosion stroke and the explosion timing thereof by using the cylinder discrimination signal outputted for every one revolution of the cam shaft of the internal combustion engine, the crank angle signal outputted for every revolution of a certain angle of the crank shaft, and the like, and drives the variable orifice a certain time before the estimated explosion timing so as to change the dynamic spring constant of the whole active mount.
By the way, in the case of a variable vibration isolating support device obtaining a desired vibration isolating characteristics by selectively introducing the intake tube negative pressure and the atmosphere, such as a liquid sealing type vibration isolating device described in the above mentioned Japanese Utility Model Application Laid-Open (JP-U) No. Hei44-77041, if the intake tube negative pressure is introduced after the atmosphere has been introduced, the atmosphere in the variable vibration isolating support device flows into the intake passage on the down stream side of the throttle valve through the negative pressure passage, so that the amount of the intake air of the internal combustion engine may be increased. When the amount of the intake air is increased, the amount of the fuel injection is also increased accompanied with that, and consequently, the engine speed of the internal combustion engine is raised.
Especially, in a case where the internal combustion engine is in the state of idling and the control of the engine speed by the ISCV is performed, the fresh air of a flow rate more than that controlled by the ISCV flows into the internal combustion engine by the operation of the variable vibration isolating support device, and the idling speed is raised to a speed not less than the desired target idling speed, and problems of giving adverse effects to the operational characteristics, the fuel consumption rate, and the like of the internal combustion engine, are produced.
Furthermore, in the liquid sealing type vibration isolating device described in Japanese Utility Model Application Laid-Open (JP-U) No. Hei4-77041, the control is performed such that the atmosphere is introduced when absorbing variable comparatively high frequency vibrations, and the negative pressure is introduced when damping comparatively low frequency vibrations. However, in the case of a V-type internal combustion engine, since the angle and the timing at which the vibrations are inputted into the vibration isolating device, are different depending on whether the vibrations are those produced by the explosion of the gaseous mixture in the cylinders of the bank on one side or those produced by the explosion of the gaseous mixture in the cylinders of the bank on the other side, there is such a problem that when using the liquid sealing type vibration isolating device, the vibrations of a V-type internal combustion engine cannot effectively be restrained.
In a variable vibration isolating support device which changes the vibration isolating characteristics by selectively introducing the atmosphere and the negative pressure, when moving from the state where the negative pressure is continuously introduced to the state where the atmosphere and the negative pressure are alternately introduced at a specified ratio, the degree of negative pressure in the air chamber is gradually decreased, and just after the movement, the diaphragm vibrates at a place near the wall surface, and therefore, there is such a problem that hammering noises are produced by the collision of the diaphragm and the wall surface.
Furthermore, in the active mount described in Japanese Patent Application Laid-Open (JP-A) No. Hei6-16050, considering that the ignition timing of each cylinder is the same timing, that is, considering that the explosion timings of all cylinders are the same timing, the dynamic spring constant of the active mount is changed a certain time before the explosion timing thereof. On the other hand, in Japanese Patent Application Laid-Open (JP-A) No. Hei3-124967, an internal combustion engine in which the fluctuation of the engine speed at the time of idling is restrained by compensating the ignition timing for every cylinder, is disclosed. When the active mount is applied to an internal combustion engine like this, it is possible that the timing to change the dynamic spring constant deviates from the ignition timing of each cylinder, and there is such a risk that the idling vibration of the internal combustion engine cannot effectively be restrained.